Emoji are a terrible insult to the written word. They're also an affront to imagery.
Standard images, at least, are the same image everywhere. A grid of pixels is a grid of pixels.
Emoji, however, vary from platform to platform, so what you pick may well not be what your reader sees. In some cases that may matter, in others it may not.
Furthermore, some people construct new meanings and usages for emoji that do not align with the actual descriptions from the Unicode standard. You'll only realize this if they tell you, of course. I had one of those moments with my wife a few weeks ago.
I'm still (irrationally) upset that emoji are in Unicode. They're ambiguous, ill-defined, and they are certainly not characters in the multilingual support sense of the word.
Do I use them? Yes, grudgingly, and I hate myself a little bit every time I do it.